When I think of ASUS and Android, the first thing that comes to mind is their past portfolio of Android tablets. ASUS has been making Android tablets since the first wave of Android Honeycomb tablets hit the market. Back then, ASUS's point of differentiation from all the other Android tablets with essentially the same Tegra 2 hardware platform was their attachable keyboard dock. One could argue that ASUS really pioneered the 2-in-1 tablet form factor with their Transformer tablets.

While ASUS continued to release a number of additional Transformer tablets with updated specifications for some time, it has been a while since we've seen any new high end tablets from the company. Recent offerings have usually been more budget oriented devices like the MeMO Pad series, or the hard to find ASUS PadFone, with the spot for a more standard tablet being left unfilled.

Today's review takes a look at a tablet that doesn't pick up where the Transformer series left off, but instead kicks off a new line of tablets from ASUS under the ZenPad brand. There are a few different ZenPad tablets on the market, with multiple SKUs for each product creating even more versions. The tablet I'm looking at today is the ASUS ZenPad S, and more specifically, the ZenPad S Z580CA, which is ASUS's most high end tablet offering. Since the ZenPad S comes in two different versions I've laid out both of their specifications in the chart below so you can get an idea of how the two devices differ from each other.

	ASUS ZenPad S 8 (Z580C)	ASUS ZenPad S 8 (Z580CA)
SoC	Intel Atom Moorefield Z3530 4x Silvermont @ 1.33GHz	Intel Atom Moorefield Z3580 4x Silvermont @ 2.33GHz
GPU	PowerVR G6430 @ 457MHz	PowerVR G6430 @ 533MHz
RAM	2GB LPDDR3	4GB LPDDR3
NAND	32GB + microSDXC	64GB + microSDXC
Display	7.85" 2048x1536 IPS LCD
Dimensions	203.2 x 134.5 x 6.6mm
Mass	298g
Camera	2MP Front-facing 5MP Rear-facing	5MP Front-facing 8MP Rear-facing
Battery	15.2Wh
OS	Android 5.0 Lollipop with ASUS Zen UI
Other Connectivity	802.11b/g/n + BT 4.1, GNSS, 3.5mm audio	802.11a/b/g/n/ac + BT 4.1, GNSS, 3.5mm audio
USB Connector	Micro USB	USB Type-C
Price	$199 USD	$299 USD

There are two versions of the ZenPad S. The less expensive model is priced at $199 USD, while the more expensive model that I am reviewing is $299 USD. This is not unlike the price split between the two versions of the ZenFone 2. However, while the two versions of the ZenFone were differentiated only by their RAM, NAND, and included charger, the two models of the ZenPad S have more differences than similarities as far as their specifications go.

What's shared between both devices is the 7.85" 2048x1536 display. ASUS advertises it as 8.0" but measurements of the display's diagonal show that there is some rounding going on. In addition to the display, both devices have a 15.2Wh battery. At $100 more, the ZenPad Z580CA doubles your RAM and storage to 4GB and 64GB respectively, increases the resolution of both cameras, bumps the max CPU clock by 1GHz and max GPU clock by 76MHz, and adds 802.11ac support.

The one thing that sets the ZenPad S Z580CA apart from most other devices is its use of the new USB Type-C connector, along with support for USB 3.0 speeds of 5Gbps (Superspeed). While we have seen USB 3.0 featured on some past devices such as the Galaxy Note 3, the large size and unsightly appearance of the USB 3.0 Micro-B connector resulted in it receiving almost no market adoption. It's important to note that just because a device uses the USB Type-C connector does not mean that it supports USB 3.1 Gen 2 (Superspeed+) along with all the USB alternate modes for networking or display interfaces. With the ZenPad S Z580CA only supporting USB data, you cannot do video out or use any other USB alternate modes. Such features will have to wait for future SoCs and controllers with USB 3.1 and USB alt mode support.

As for the connector, Type-C is slightly larger than your standard Micro-B port in all dimensions, but it's reversible, more durable, and maintains a much stronger connection to a device. You can insert it in two orientations, and when you push it in there's a click to let you know that it connected. Some users will see the adoption of USB Type-C as a nuisance, as it will prevent them from using existing cables to charge the tablet or transfer files. I personally recognize this as an unavoidable transition period, as there's no chance of every vendor and user in the world deciding to move to Type-C all at once. It's obviously a bit of an annoyance to be unable to use existing Micro-B cables, but I believe the advantages are worth it.

The ZenPad S uses ASUS's ZenUI skin for Android. It's basically the exact same UI as on the ZenFone 2, but with some layout and app design changes to work better on the larger display. For a look at ZenUI I recommend looking at the software section of my ZenFone 2 review, as I won't be discussing it in this review due to it being mostly redundant.

Design

In my mind, I think of the ZenPad S Z580CA as a companion to the ZenFone 2. Both devices have an affordable price, and you can really buy both of them and still end up spending less than you would on a flagship smartphone. While they definitely share a UI and many internal hardware components, there isn't much similarity between the external design and construction of the two devices.

The first thing you'll notice when you pick up the ZenPad S isn't how the materials feel, but how incredibly thin and light the entire device feels. It's 6.6mm thick at its thinnest point, and the thickest point is only a small fraction of a millimeter thicker than that. Its mass is only 298g, which makes it the lightest tablet I've looked at to date. While it's not as thin as the iPad Air 2 or the Dell Venue 8 7840, the thickness and mass work together to give a feeling of lightness and portability that I've only ever experienced with one other device, which was the original iPad Mini.

There's not much to say about the front of the ZenPad S. Like all tablets, it's just a big display. ASUS has made space for two front-facing stereo speakers, which is something you won't get on an iPad or on the Galaxy Tab S2. As for the quality of the speakers, my highly subjective evaluation is that they are better than the iPad Air 2, and much better than the Nexus 9. They also don't cause significant chassis vibration despite the tablet's small thickness, which is something the iPad Air 2 suffers from.

Surrounding the edge of the ZenPad's front bezels is a metallic looking silver edge. This is really made of plastic, and like the plastic construction of the ZenFone 2 I'm a bit concerned about its durability. Readers may remember that a single fall from an extremely short height ended up scuffing up the back cover of our ZenFone 2 pretty badly. With the ZenPad S I have made sure to be quite careful, and haven't dropped it or hit it off anything to the best of my knowledge. Even so, there are some small dents in the silver edge. Pressing on it confirms that it's a fairly soft plastic, and I feel like it's going to be a magnet for these types of small dents and marks. In contrast, the Nexus 9 and iPad Air 2 testing units I have could probably be packaged and sold as brand new despite having them in my possession for significantly longer than the ZenPad S. If someone intends to use the ZenPad S as a tablet they can throw into their bag with other objects I would definitely be aware of the potential for damage to the edge.

The back of the ZenPad S is split into two sections. The smaller section has a soft touch feeling, and almost feels a bit like the pleather some phone cases are made of as it has a texture to it. This section is slightly thinner than the rest of the back cover, and it houses the tablet's MicroSD slot. What's interesting is that this part blends smoothly into the sides of the tablet, even though the sides have a distinctly different feeling due to their lack of texture. The soft touch part of the tablet also has the tablet's name and the Intel logo on it. However, it rubs off fairly easily as you can see in the image above, and at the time of writing this paragraph the logos have come off entirely.

The second part of the ZenPad back cover is a large plastic panel. In my review of the ZenFone 2 I said that the back cover of the phone did a good job of mimicking the appearance of aluminum, but felt entirely like plastic. The plastic segment of the ZenPad's back cover could actually convince you that it's made of metal unless you have the urge to tap on it. Like the ZenFone 2, the ZenPad's back cover has a shine to it that looks very much like the reflections made by brushed aluminum, although in the ZenPad's case the back cover has a pattern of overlapping diagonal lines rather than the straight lines of the ZenFone 2. Unfortunately, the hard plastic part of the back cover doesn't give any illusion of the tablet itself being made of metal, as you'll always be touching the soft touch plastic of the sides and the smaller segment of the back.

Right out of the box, my ZenPad S review unit did seem to have some issues with the hard plastic segment of the back cover that I think should have been picked up during QA. As you can see in the images above, there are areas on the edge of the plastic that are warped in such a way that they are no longer smooth like the other sections. It looks like these areas weren't finished properly, and when you look at the tablet from the side you can see that the entire edge around the power button and volume rocker is improperly formed and doesn't have the same color as the rest.

Ultimately I think the ZenPad S does a good job at being what it is, which is a tablet with a plastic chassis. My big concern is that the iPad Mini 2 sits at exactly the same price, and offers a completely aluminum chassis that feels much higher quality and will likely not incur the damage I've seen on the ZenPad's edge and back cover. The iPad is obviously heavier and thicker though, and the only way to achieve the low mass that the ZenPad S has is with plastic.

Personally, I think if I was given the choice I would opt for a slightly thicker and heavier device made of aluminum or a more durable plastic than a thinner and more easily damaged plastic one. The thicker device also has the benefit of storing a larger battery. Other people may value the thinness and the lightness more, particularly with 8" tablets which are more likely to be kept on someone's person than larger tablets. In the end everything is a series of trade-offs, and it's important to think about what aspects of design and build quality matter most to you when considering which tablets to buy.

System Performance

A common trend among the tablets I've reviewed in the past few months is that they've used Intel's mobile SoCs rather than the ARM SoCs that you'll see in most tablets and smartphones. All the tablets I've reviewed have come from manufacturers that traditionally made Windows PCs and laptops, and the long-term relationship they would have with Intel is a reasonable explanation as to why they've partnered with Intel for the processors in their tablets. Like both models of the Dell Venue 7000 series, and the top tier model of the ZenFone 2, the ZenPad Z580CA is powered by an Intel Atom Z3580 SoC. This is a quad core Atom part built on Intel's 22nm process, with a max burst frequency of 2.33GHz. In the case of the Z580CA it's paired with 4GB of LPDDR3-1600 memory, which is twice as much as the amount in the Dell Venue tablets.

To evaluate the ZenPad Z580CA's performance I've run it through our standard benchmark suite. The first set is our web benchmarks which is influenced both by a device's browser optimizations as well as its CPU, followed by BaseMark OS II to evaluate several aspects of a device's hardware, and finally PCMark which emulates tasks that a user would perform while actually using a device.

The ZenPad S performs well in our web browser benchmarks. There’s clearly differences at the OS level as well as possible BSP (board support package) differences between the ZenPad and other Intel-based Android devices like the Dell Venue tablets and the ZenFone 2. In Kraken we see a result closer to the middle of our chart, sitting among the Venue 8, Venue 10, ZenFone 2, and Apple’s A7-based iPads. It’s worth noting that as we no longer have those iPads for testing, the results for those devices were performed on iOS 7 and don’t benefit from any enhancements made to Apple’s rendering engine in subsequent releases.

In Google’s Octane benchmark the ZenPad S sits high on the chart with a score that isn’t quite as high as the Nexus 9 or the iPad Air 2, but sitting not far behind. There’s an enormous improvement over the ZenFone 2, and I’m not sure what to attribute this to as both devices use the same hardware platform and both are Android 5.0 underneath ZenUI. Since the test isn’t very long it’s not likely that it has to do with differences in thermal throttling between the two, and most likely is rooted somewhere in the software differences between the ZenFone and the ZenPad.

As for the 2013 and 2015 iterations of WebXPRT, the ZenPad S seems to perform much better in the latter test than it does in the former. While in WebXPRT 2013 it sits behind the iPhone 6 and the Nexus 9, in the 2015 iteration it surpasses both of them. In both cases it’s still behind the iPad Air 2, but for $299 you’re getting a lot of performance for your money.

Like all the Intel-based Android devices that I’ve tested, the ZenPad S doesn’t score very high in BaseMark OS II. The score in the graphics sub-test is tied with all the other G6430 devices for last, which says more about how far GPU performance in mobile has come in two years rather than the ZenPad S simply being slow. The score in the system sub-test which stresses the CPU and RAM is the lowest on the chart. In the end all Intel Atom devices don’t perform well in BaseMark OS II, but when a device is $199 like the ZenFone 2 or $299 like the ZenPad S Z580CA I think the performance that the Atom SoC provides is more than sufficient.

Our final test is PCMark, which emulates tasks that users will perform in the real world like browsing the web, playing and seeking videos, editing photos, and more. The ZenFone 2 performed very well in PCMark, but it ended up being carried to an extent by a disproportionately high photo editing score. The ZenPad S takes this even further with a higher photo editing score, and ends up taking the top spot in the overall ranking. There’s definitely a large software influence in these tests, which isn’t unlike the real world performance that is being tested, which requires both good hardware and optimized software to provide good performance. That being said, I think the ZenPad S ranking first on the basis of its extremely high photo editing score is a little bit questionable, but even without that test it would still score highly overall.

My conclusions about the system performance of the ZenPad S Z580CA are not unlike those in my ZenFone 2 review. When a device is $199 or $299, Intel’s Atom Z580CA SoC is faster than any ARM-based Android device at that price. PCMark doesn’t support iOS, and so there’s no way to know how well the ZenPad S compares to the iPad Mini 2 outside of web performance, but based on the JavaScript benchmark results it’s clear that the ZenPad S should be competitive with it, if not faster.

GPU Performance

Rather than using Intel’s HD series iGPUs, the Atom Z3530 and Z3580 SoCs in both versions of the ZenPad S use Imagination Technologies’ PowerVR G6430 GPU. Since this implementation is identical to the one in the ZenFone 2 it’s not likely we’ll see a large gap in absolute performance. However, the larger chassis of the ZenPad may allow it to dissipate heat more effectively, which could help performance in long-term sustained workloads. It’s also worth noting that the less expensive Atom Z3530 model of the ZenPad S will suffer from reduced performance in GPU heavy workloads due to the 1GHz reduction in max CPU clock compared to the $299 model, as well as the drop in GPU speed from 533MHz to 457MHz.

In 3DMark we actually see a noticeable gap between the ZenPad S and the ZenFone 2. The latter ends up scoring around 2000 points higher in both sub-tests, which leads to an overall score which is also around 2000 points higher. I would mostly attribute this to software differences rather than any issues with throttling, and the next tests will help to confirm that assumption.

The ZenPad S doesn’t perform as well as the ZenFone 2 in BaseMark X’s on screen tests, which isn’t surprising given that it’s pushing 1.6 million more pixels. In the off screen tests we see both devices perform roughly equally, and this is reflected in the overall score. In other reviews, such as my review of the Dell Venue 8 and Venue 10 I mentioned that G6430 is a bit slow compared to the competition at that price point. For a $299 it fits perfectly, and coincidentally a lower clocked version of it is what’s used in the iPad Mini 2 which is also $299.

In GFXBench we again see the ZenPad S performs worse than the ZenFone 2 at its native resolution, but the overall GPU power of the two devices is equal. Like the Venue 8 and Venue 10, the PowerVR G6430 implementation in Atom Z3580 outperforms Apple’s A7 by a significant degree in the T-Rex HD test, but not in any other.

It’s clear from our tests that the GPU performance of the ZenPad S Z580CA is roughly the same as Apple’s iPad Mini 2. Since both devices have the same price, the ZenPad S is right where it needs to be in this regard. Performance in programs running at a device’s native resolution will obviously be slower than the ZenFone 2 due to the ZenPad S’s higher resolution, but I think G6430 provides more than adequate performance to run the display, and is the best you’ll be able to find in a $299 device right now.

NAND Performance

The performance of a mobile device's internal storage can have a significant impact on performance. When any applications are performing reads or writes in the background, a low NAND solution can cause the tasks the user is currently performing to grind to a halt. On top of that, there are fairly obvious implications for the time it takes to move music, movies, pictures, and other media to and from the device.

Both random read and random write speeds on the ZenPad S are very good for a mobile device. In both cases it ends up being the fastest tablet on record.

The sequential read speed on the ZenPad S is good for a $299 device, and the sequential write speed is actually the fastest we've seen in an Android tablet. However, it's disappointing to see that Android devices can now adopt USB 3.0 without terrible connectors by using USB Type-C, yet they still have NAND that won't even saturate a USB 2.0 link in the best possible scenario. Relative to the NAND in other Android devices the ZenPad S performs well, but the speed of eMMC flash memory still leaves much to be desired.

Display: Stock Settings

I often say that a smartphone is just a display you interact with, which makes the need for a high quality screen paramount. This is even more true for tablets, which are quite literally large touchscreen displays that the user interacts with. With tablet displays having peaked in terms of resolution for the time being, manufacturers are now turning their attention toward color accuracy. Flagship devices like Samsung's Galaxy Tab S tablets and Apple's full sized iPads feature displays with an exceptional level of color accuracy, while smaller or less expensive tablets are more hit-and-miss.

Unsurprisingly, the ZenPad's display is very similar to that of the iPad Mini 2 as far as brightness, black level, and contrast are concerned. While Apple has decided to round 7.85" to 7.9", and ASUS has decided to round to 8.0", I'm fairly confident both devices are using the same LCD technology with different backlight arrays. It should be noted that while the contrast ratio is similar in our measurements, when there is ambient light there will be a much more significant drop in contrast on the iPad Mini 2 due to its unlaminated display.

Even if two devices use the same display panel, the color characteristics of each can vary significantly depending on the level of calibration, as well as the spectral range of the LED backlight used. Apple’s iPad Mini 2 achieves a level of greyscale accuracy where errors can only be seen in static content, and is good enough for editing photos and videos without concerns about the accuracy of the images. The ZenPad S doesn’t do as well, with a significant blue shift to most shades of grey. This is also reflected in the display’s high average white point of 7331K. While the ZenPad S doesn’t cost as much as an iPad Air 2 or a Galaxy Tab S2, the Z580CA’s price of $299 is exactly the same as the iPad Mini 2. With that in mind, it’s concerning to see such a gap between the greyscale performance of the ZenPad S and the iPad Mini 2.

Saturation accuracy on the ZenPad S is much lower than what could be achieved with more attention paid to the display’s calibration. With a DeltaE average of 6.2, the ZenPad S is actually less accurate with rendering primary and secondary colors than the iPad Mini 2, despite the latter having a backlight array that only allows for narrow coverage of the blue and red parts of the sRGB gamut. The spectral range of the LEDs in the ZenPad S almost covers the entire sRGB gamut, but the panel undershoots significantly with reds, overshoots with blue beyond 60% saturation, and has various levels of inaccuracy with yellow, cyan, and most of all, magenta. I was really excited to see that the ZenPad S doesn’t suffer from the narrow gamut of the iPad Mini 2, but I was let down when I realized that the accuracy of primary and secondary colors was actually worse than the iPad due to inadequate calibration.

Accurately reproducing color mixtures requires a reasonably accurate gamma, RGB balance for grey shades, and accurate saturations. Gamma on the ZenPad S is reasonably accurate for a mobile device, but the way the display tends toward blue coupled with the inaccurate saturations results in inaccurate color mixtures as well. The ZenPad’s average DeltaE of 5.55 doesn’t compare favorably with the iPad Mini 2’s DeltaE of 3.4 which is imperfect but still fairly accurate. The reason that the iPad Mini 2 ends up being more accurate is because while it cannot be accurate outside its native gamut, within the section of sRGB that it does cover it is very accurate.

As far as the default display configuration of the ZenPad S goes, I’m not exactly thrilled. While it does have a wider gamut than the iPad Mini 3, it ends up being less accurate in every respect due to issues with rendering primary and secondary colors, and a blue shift in the greyscale. Surprisingly, the ZenPad S having a fully laminated display has done nothing to reduce black levels and increase contrast ratio when compared to the non-laminated iPad Mini 2 display, which is an additional disappointment. However, ASUS does provide a few settings to tweak the display, and so hope is not lost.

Display: Altered White Point

ASUS’s ZenUI devices include an application called Splendid, which allows the user to select from a few different display settings or create their own. The controls are limited to a color temperature slider, a hue slider and a saturation slider. Because there’s absolutely no way for a normal user to check if the adjustments they are making are improving or reducing the display’s accuracy, I’ve refrained from adjusting the hue or saturation sliders. However, users can judge when adjustments to color temperature have made the rendition of grey shades less cold than the stock settings, and so I have adjusted the color temperature slider to be 3 positions from the right for the following tests.

As you can see above, adjusting the white balance allows the ZenPad’s greyscale accuracy to increase dramatically, and the display’s blue shift is essentially eliminated. The accuracy is now competitive with the iPad Mini 2, which is where it really should have been in the first place. Adjusting the color temperature to this setting does drop peak brightness by 8 nits or so, but it’s well worth it to improve the appearance of the display to this extent.

Before adjustment on the left, after on the right

Saturation accuracy improves from being less accurate than the iPad Mini 2 to being noticeably more accurate. There’s only so much that can be done by adjusting the display’s overall RGB balance, and I really wish the ZenPad S had better accuracy than this right out of the box, but it’s still a good improvement from the stock settings.

Before adjustment on the left, after on the right

In the GretagMacbeth ColorChecker test there’s a good improvement in the accuracy of color mixtures with the adjusted color temperature. Since the saturation accuracy is still imperfect, there’s inherent error to many of the color mixtures, but the error is to a much lesser degree than how the display looks without any adjustments.

In the end the ZenPad S has a better display than ASUS’s default settings would have you believe. Although the ZenPad S has a laminated display and a wider color gamut than the iPad Mini 2, based on the results of the ColorChecker test I would have to conclude that the iPad Mini 2’s display is superior overall. If you can adjust your ZenPad’s display you will still have a very sharp panel, and in the $199 model it’s definitely best in class. That being said, I think the $299 ZenPad S Z580CA should have aimed higher when it comes to color accuracy, as the two year old iPad Mini 2 still offers better reproduction of grey shades, colors, and offers roughly equivalent brightness and contrast.

A Word On ASUS VisualMaster/True2Life+

The ZenPad S Z580CA comes with a number of display "optimizations" which are similar to those you would find on televisions. I put optimization in quotes because while it is true that slight adjustments to brightness and gamma can help to maintain image quality in different ambient conditions, I have never in my entire life seen a single device where those optimizations are applied in a reasonable manner. The display oriented processing that ASUS performs is marketed as ASUS True2Life+ technology, and I wanted to go over a few aspects of it while also discussing the positive or negative impacts they had on my experience when using the ZenPad S.

Dynamic Brightness and Contrast

These features are often referred to as CABC, or Content Adaptive Backlight Control. ASUS advertises them as a measure to improve image quality, but in practice it's more useful as a tool to save power when applied in the right situations. Unfortunately, the ZenPad S goes overboard with its adaptive brightness, which was also an issue with the ZenFone 2. Because the ZenPad S has a much larger display, the shifting of brightness is far more obvious than on a phone. For example, when scrolling through the recent apps tray you will notice the brightness of the entire display going up and down depending on how light or dark the interface of the application currently in view is. Swiping open the quick toggles in the notification shade also changes the brightness of the display, as do many of the switches to and from applications. A tablet like the iPad Air 2 employs the use of CABC when watching videos, and even in that case I am still not a fan but I understand the purpose. Having significant brightness changes constantly occurring throughout every app and every part of the UI is not something I understand, and it's not something that I feel devices should use outside of something like a power saver mode or when the display APL is incredibly low.

Sharpening

This part of VisualMaster is fairly self explanatory. ASUS performs sharpening as a post-processing effect, and it applies to pretty much all content on the display to varying degrees. I have never seen this feature implemented in a way that is completely useful, and the ZenPad S is no exception. Like other devices that perform sharpening, like the LG G3, the only thing I notice is that text and any objects made of reasonably thin lines has a distracting halo effect. It seems contradictory to the idea of sharpening, but the effect actually reduces the sharpness of what you see on screen, and at times it can actually cause small text to be straining on the eyes. Considering the ZenPad S has a 326ppi display, I don't understand why there's any need for artificial sharpening. To my knowledge, there's no way to disable this feature, so it's something users will have to deal with unless ASUS issues an update with an option to disable it.

Blur-free Motion

The last significant aspect of VisualMaster/True2Life+ is ASUS's Blur-free motion tech. This is essentially the same as the frame interpolation that you see on televisions, which analyzes two frames and attempts to construct an intermediate frame that would go between the two. This feature is actually very successful in making videos appear to be a higher frame rate than they actually are, and it does help to eliminate blurring. I'm actually quite impressed that this can be done as a real-time processing effect on a performance-limited device like a tablet without significant artifacting or other issues. That being said, I fundamentally disagree with the entire concept. To be clear, I am not at all against filming or animating video content at a frame rate higher than 24fps. What I am against is the idea of trying to make content that was not produced at a high frame rate look as though it was. I've loaded as many different videos as possible onto the ZenPad S, and because I'm used to seeing all of them run at 24 or 30 frames per second they just look strange with ASUS's anti-blur processing and frame interpolation.

Unlike the display's heavy CABC, ASUS offers a setting to disable the anti-blur processing in the display section of the settings application. When I first received my review unit, this setting was actually broken which was a huge issue. A recently released firmware update which brings the tablet to V4.1.0 fixed this issue, which is a huge relief. I personally would recommend turning this feature off, but it's great that users are given the option of having it if they want it.

Final Words

Ultimately, I've never seen much appeal in the heavy post-processing that televisions can apply to content, and that hasn't changed with it being brought over to mobile. Most of my feelings toward VisualMaster and True2Life+ are negative, and I really wish there was an option to just turn all the processing off entirely.

Camera

While most people will use either their smartphone or a dedicated camera for taking photos, a tablet can be used in a pinch. Some people even make their tablet their primary camera, whether it be because it's their only device, or because they prefer the larger viewfinder that a tablet offers. While many may still find the idea of taking photos with a tablet to be absurd, one need only look at the people around them to see that for one reason or another tablet photography has become a way that some users choose take photos.

The ZenPad S Z580C sports a 5MP rear-facing camera, and the Z580CA bumps that to an 8MP sensor. Since resolution is only one of many aspects of a device's camera system, I've included some more information about the ZenPad S Z580CA's cameras in the chart below

ZenPad S (Z580CA) Camera Specifications
Front Camera	5MP (2592x1944)
Front Camera - Sensor	Omnivision OV5670 (1.12 µm, 1/5")
Front Camera - Max Aperture	F/2.4
Rear Camera	8MP (3280x2464)
Rear Camera - Sensor	Toshiba T4K35 (1.12 µm, 1/4")
Rear Camera - Focal Length	3.0mm (28mm eff)
Rear Camera - Max Aperture	F/2.0

The ZenPad has a similar camera stack to the ZenFone 2. Toshiba's T4K35 sensor has a resolution of 8MP with 1.12 micron pixels, while the ZenFone 2 used T4K37 which had the same pixel size but a higher 13MP resolution. Lens aperture and focal length end up being the same as the ZenFone 2 as well.

To evaluate the still image quality of the ZenPad S I've taken photos of my standard photo scene during the day and at night, and compared the results to the other tablets that I have available for testing which includes the Nexus 9, the iPad Air 2, and the Dell Venue 10 7040.

It's clear that the ZenPad S suffers from the exact same processing issues as the ZenFone 2. There's far too much sharpening of the image as well aggressive noise reduction. This can be easily seen in any of the foliage in the frame, and in the lines separating the bricks of the school walls. There's also noise across the entire sky, despite this photo being taken with enough light for the camera to shoot at the base ISO of 50. The still image section of my ZenFone 2 review goes into more detail on these issues, and it's disappointing to see that none of them have been resolved. Relative to the other tablets in my comparison, I would have to say that the ZenPad S takes the lowest quality photos. The exposure and color accuracy is much higher than the Dell Venue 10, but the extreme oversharpening and heavy noise reduction makes the image look more like a painting than a photo.

In low light the ZenPad S continues to perform poorly. Low light scenes really make it clear how much of a photo's quality has to do with the quality of the image processing performed. Both the Nexus 9 and iPad Air 2 share a sensor size and resolution with the ZenPad S, and both actually have smaller apertures. Despite this, they both have a better exposure and a much greater level of detail than the ZenPad S. Unlike the day photo test, I would say that the ZenPad S did take a better photo than the Dell Venue 10, but only because I can't even begin to describe the problems with the Venue 10's photo.

Ultimately, the ZenPad S suffers from the exact same issue as the ZenFone 2, which is poor image processing. The color rendition and exposure of images taken during the day makes it clear that the camera has potential, but the numerous issues with the processing produces poor quality images.

WiFi Performance

Like the ZenFone 2, the ZenPad S Z580CA uses Broadcom's BCM4339 WiFi + Bluetooth solution for wireless connectivity. The implementation in the ZenPad S supports two spatial streams on 802.11ac, which allows for a peak theoretical link speed of 867Mbps. However, the ZenPad S has a software problem that makes real world speeds significantly lower than that.

You may be wondering why the ZenPad S can only get a maximum speed of 173Mbps over UDP when the ZenFone 2 with its 1x1 802.11ac goes as fast as 293Mbps. You may have also noticed that a speed around 150Mbps is very similar to devices with 2x2 802.11n WiFi, and that's exactly the problem. The ZenPad S only works in 802.11n mode, a software problem that should have been found in testing long before the tablet actually shipped. I have tested the ZenPad S with an Apple Airport Extreme 6th gen and a TP-Link Archer C7, and the max link speed remains at 200Mbps in both cases. ASUS has confirmed the issue on their end and is aware of it, and so a software fix should arrive for it at some point. Users are, at the moment, just going to have to live with WiFi that isn't even half as fast as it would be if it was working properly.

Battery Life

The first generation of the iPad promised a ten hour battery life, which was exceptional when one considers what the battery life of smartphones and laptops was at that time. Since that time the battery life target OEMs aim for with tablets has usually hovered around that 10 hour mark. Whether or not a tablet lasts that long obviously depends on a mixture of the user's workload and the OEM's honesty in the battery numbers they report. As for the ZenPad S Z580CA, its 15.2Wh battery is rated for up to 8 hours of battery life by ASUS, which is lower than I would expect when the iPad Mini 2 is competing at the same price with a 10 hour battery life. Of course, the ZenPad S is 0.9 thinner at its thinnest point, which leaves less room to put in battery. This may be one of the cases where I would agree that a thicker device with a larger battery would be better, but that will depend on the outcome of our battery tests.

As always, all devices are calibrated to 200nits for all battery benchmarks, and they follow the standard order of web browsing, BaseMark OS II, PCMark, and finally GFXBench 3.0.

In our WiFi web test the ZenPad S falls about 43 minutes short of its rated 8 hour battery life. Had it been designed for a 10 hour rating this wouldn't be a huge deal as you'd still be talking about nearly 9.2 hours of battery life. However, 7.18 hours is a relatively short battery life for web browsing when you consider that the iPad Mini 2 lasts 9.83 hours in the same test, while the Dell Venue 8 7840 lasts 9.59 hours with the same SoC and a similar display area.

The ZenPad S does fairly well in BaseMark OS II's battery benchmark which mainly stresses a device's CPU. However, it's again outclassed by the Dell Venue 8 7840 which uses the same SoC and actually has a thinner chassis. In this case I would say that the ZenPad S doesn't have bad battery life at all, but I do wish it was a bit higher than it is.

The ZenPad S achieves the shortest battery life of our tested devices in PCMark's battery life test. Although both devices are close, its battery life is slightly shorter than that of the Dell Venue 10 7040, which I repeatedly noted as having extremely poor battery life. PCMark is a fairly good example of the battery life that a user can expected from a mixed workload, and the ZenPad S Z580CA's battery life of 5.33 hours is not quite where it needs to be.

The ZenPad S doesn't last quite as long as the iPad Air 2 in GFXBench's battery test, and sits a little more than 46 minutes behind the Dell Venue 8 7840. Evaluating how well a device does in GFXBench requires considering both the battery life as well as the performance. A device can last a long time but deliver performance that isn't even remotely playable. Conversely, a device can last a short time but have incredible performance, which would still be preferable to a long period of unplayable performance.

With a steady frame rate slightly above 19 FPS for most of the test, the ZenPad S doesn't quite offer smooth performance during the 3.69 hours that it ran for. In comparison, Apple's iPad Air 2 lasted longer and approaches upon 50 FPS, which is well above the 30 FPS that many 3D mobile games target. However, it's also worth noting that this is an on-screen test, and in games that render below a device's native resolution it's entirely possible that the ZenPad S would deliver smooth performance while maintaining its 3.69 hours of battery life. It's also worth noting that the iPad Air 2 costs significantly more than the ZenPad, and while we don't have information about the iPad Mini 2 in this test, it's very likely that its performance would be similar. In the end, the PowerVR G6430 GPU is still a fairly capable GPU, even if it can't run intensive 3D games at 2048x1536. I think the GPU performance and battery life in GPU heavy loads that the ZenPad S offers is more than acceptable for a $300 device.

Charge Time

Since tablets have significantly larger batteries than smartphones, they have always required high power chargers to recharge their batteries in an acceptable period of time. Even so, devices like the 2012 iPad took as long as six hours to charge even with a 10W charger due to the sheer size of their battery. Thankfully, reductions in platform power have allowed for smaller batteries while maintaining battery life, which leads to shorter charging times for tablets. At the moment, most tablets seem to take between 3.5 and 4 hours to charge, and with its 15.2Wh battery one would hope that the ZenPad S could go below that 3.5 hour figure. As you can see above, the ZenPad S doesn't quite meet that goal.

The ZenPad 2 charges slightly quicker than other tablets like the iPad Air 2, iPad Mini 2, Nexus 9, and the Galaxy Tab S 8.4. However, it doesn't charge as fast as the Dell Venue 8 7840. To be honest, I had expected a better result here because of the ZenPad's relatively tiny battery capacity. Dell's included charger provides 7W of power, which isn't as much as the 10W+ bricks that come with iPads and some other tablets. It's worth noting that I also checked the charge time when using ASUS's 18W QC 2.0 power brick, but measured no difference from the one that comes in the box. I would like to note that the lack of QC 2.0 support has absolutely nothing to do with the use of the USB Type-C connector. The USB connector is unrelated to the data and power protocols.

In the end users won't be getting a significant shorter or longer charge time than other tablets, but knowing that the battery is only 15.2Wh has me feeling a bit let down that the ZenPad S takes as long as it does to charge.

Final Words

As I said in the introduction, its been a long time since we've seen a tablet from ASUS that wasn't aimed at the low end of the market. The ZenPad S Z580CA isn't a $500 flagship tablet, but with the specifications it provides it's essentially a high end 8" Android tablet. Like the ZenFone 2, its $299 price would have you believe that its specifications are less impressive than they really are. However, it's really impossible to judge a device solely based on how it looks on paper, even when what you seen on a spec sheet looks appealing. Over the course of reviewing the ZenPad S I've encountered aspects of it that are good, and some that need improvement. I suppose this is the best time to go over everything once more before making some conclusions.

The ZenPad S does a good job of making a plastic chassis feel solid and high quality. The hard plastic on the back does a better job of emulating the feeling of metal than any other device I've used before. I personally would have not opted to make the sides and part of the back cover out of a soft touch plastic, because it introduces seams and breaks in the chassis which is detrimental to the design. I also feel a bit spoiled by the fact that there are devices like the iPad Mini 2 which give you a fully aluminum chassis for $299 as well. The ZenPad ends up being thinner and much lighter than the iPad, which is certainly a benefit for any user who wants a device that they can bring everywhere without feeling like they're lugging around a heavy object. My personal use case for a tablet leads me to lean toward a thicker and heavier aluminum chassis over a thinner and lighter plastic one, but I recognize that other people may have different needs which make the ZenPad S a more appealing device in that regard.

One area where an aluminum chassis would certainly help is durability. While metal can obviously dent and scratch, my time with the ZenPad S has made it clear that there are both issues with the durability of the plastic used, and with the tolerances for defects in the materials. If I was purchasing the ZenPad S for myself I would definitely not consider the deformed edges of the hard plastic that my review unit has to be acceptable, and the same would go for the easily damaged edge around the bezel. Even without a metal chassis, other plastic tablets like the Dell Venue 10 and the Nexus 9 have held up much better over the course of weeks and months than the ZenPad S did in only a week. Durability is definitely something to keep in mind if you're fairly rough on your devices, or if you want to keep your ZenPad for a long period of time.

As far as performance goes, the ZenPad S is right in line with all the other Intel devices that I've looked at. The 4GB of RAM means that you will rarely ever see a process be evicted from memory, but with Android having no support for split screen application views it almost feels like the ZenPad S has some untapped potential. The CPU performance is just as good if not better than anything else you'll find at this price, and the 533MHz G6430 GPU ends up being slightly faster than the implementation in Apple's A7 SoC. In my reviews of Dell's Venue tablets I remarked that Atom Z3580 didn't feel competitive enough in a $400 or $500 device, but in a $300 tablet it feels right at home.

The ZenPad's display is difficult to come to a conclusion on. Out of the box the image rendition is very inaccurate, but you can make significant improvements by adjusting the color temperature. My problem with this is that I think it's wrong to offer bad default settings that the user has to fix on their own, especially when there's no way they can find the optimal setting for a display by using their eye alone. Even after adjusting the display, the overall accuracy is still significantly lower than the iPad Mini 2 despite the ZenPad S not suffering from the narrow gamut that the iPad does.

On top of the issues with color accuracy, ASUS's True2Life+ tweaks have a very negative impact on display quality. The over-sharpening causes halos around text, and when text is a small size it actually makes it more difficult to read than it would be if it hadn't been artificially sharpened, which is contrary to the entire point of sharpening. ASUS's CABC also goes way overboard, to the point where you can notice the brightness of the display constantly shifting as you scroll around and move between apps. Without True2Life+ I would still lean toward the iPad Mini 2 having a better display due to its greater accuracy with common color mixtures, even if it does have a narrow gamut and isn't laminated. Despite that, I would have said that the ZenPad S's display is still very good for a $299 device. Unfortunately, the post processing that ASUS performs really degrades image quality to the point where the ZenPad's display is not something I can highly praise.

There's not much to say about the camera quality of the ZenPad S. It suffers from all the same issues as the ZenFone 2, and I really wouldn't use it to take photos unless there's no alternative. Thankfully I don't think that the camera is a huge selling point for a $300 tablet, and so this problem isn't that serious.

Battery life on the ZenPad S was good considering the battery capacity it's working with, but not competitive with other tablets. With tablets there's really no room to have your battery life fall short, because there's been an expectation of ten hours of battery life from tablets for over five years now. In every battery category the ZenPad either doesn't last as long as competing tablets, or lasts as long or longer but with the caveat that performance over that period of time wasn't as high as the competition. I think a larger battery would have really been beneficial, even if it meant that the ZenPad S Z580CA had to be heavier and 7mm or 7.5mm thick instead of 6.6mm.

In the end I'm not as impressed by the ZenPad S Z580CA as I was with the ZenFone 2. In the case of the ZenFone 2 I actually felt that the $199 model offered the best value because you were only trading away some NAND, dropping to 2GB of RAM, and limiting the CPU clock to 1.8GHz instead of 2.33GHz. If the ZenPad S Z580C was the same sort of downgrade I would have no trouble recommending it for $199. However, you end up with significant reductions to both the CPU and GPU clocks, worse cameras, halved RAM and NAND, no 802.11ac WiFi (assuming it gets fixed on the Z580CA), and no USB Type-C connector. That's a lot of sacrifices to save $100, and the performance impact of dropping the max CPU clock to 1.33GHz would be very significant in bursty workloads.

As for the Z580CA itself, there are just a lot of issues that are difficult to overlook. The build quality and construction is just not competitive with the iPad Mini 2 or the more expensive but still relevant Dell Venue 8 7840. Much of the other issues are rooted in software, like the WiFi issue, the display issues, the camera issues, and before a recent software update, the video playback issues. While I didn't talk about ZenUI in this review, anyone who visited the link to my discussion of it in my ZenFone 2 review knows that you'll also be dealing with a large number of pre-installed apps on the ZenPad S, with most of them not being very useful. There's also still the fact that the library of really good tablet apps for Android devices is still quite small, and while this isn't within ASUS's control, it's still a very real issue to consider when you have the iPad Mini 2 competing at the exact same price.

At $299, the ZenPad S Z580CA actually doesn't have much in the way of direct competition from other Android OEMs. The $399 price point seems to be where a lot of manufacturers have aimed, with devices like the Dell Venue 8, Nexus 9, and Galaxy Tab S2 8.0 all selling for that price. With that in mind, the ZenPad S does end up being the best device at its price point, but due to a lack of competition more than anything else. If I were recommending a tablet to someone aiming to spend around $299 I would still lean toward the iPad Mini 2 if they weren't partial to Android or iOS. If someone does really need a tablet that runs Android for any number of reasons then I think it would be best to save up and take a look at the devices selling for around $400. That being said, if a user can't use a tablet that runs iOS and can't budge from a $300 price, then the ZenPad S Z580CA appears to be the best of the few options available.